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Water Resources
Water is important for several reasons.
• It keep us alive; most organisms are more than 70% water.
• It sculpts the earth’s surface and moderates the climate.
• Water removes and dilutes wastes and pollutants
Importance of Water
Click on hyperlink to view video clip
The unique properties of water are mostly due to the attractive forces between its molecules.
There are strong forces of attraction (hydrogen bonds) between molecules of water.
Attractive forces between water molecules cause its surface to contract and to adhere to and coat a solid. (cohesion and adhesion)
Water exists as a liquid over a wide temperature range because of the strong forces of attraction between mater molecules.
Liquid water changes temperature slowly because it can store a large amount of heat without a large change in temperature. (high heat capacity)
Evaporating liquid water takes large amounts of energy because of the strong forces of attraction between its molecules.
Liquid water can dissolve a variety of compounds.
Unlike most liquids, water expands when it freezes (this means that ice floats on water).
Water filters out wavelengths of the sun’s ultraviolet (UV) radiation that would harm some aquatic organisms
Water resources video clip 2
hydrologic cycle Biogeochemical cycle that collects, purifies, and distributes the earth's fixed supply of water from the environment to living organisms and then back to the environment.
groundwater Water that sinks into the soil and is stored in slowly flowing and slowly renewed underground reservoirs called aquifers; underground water in the zone of saturation, below the water table.
aquifer Porous, water-saturated layers of sand, gravel, or bedrock that can yield an economically significant amount of water.
Infiltration the movement of water from the surface through the soil and into an aquifer
Hydrologic Cycle: Key Terms
Hydrologic Cycle: Key Terms
floodplain Flat valley floor next to a stream channel. For legal purposes, the term often applies to any low area that
has the potential for flooding, including certain coastal areas. watershed Land area that delivers water, sediment, and dissolved substances via small streams to a major stream (river). recharge area Any area of land allowing water to pass through it and into an aquifer.natural recharge Natural replenishment of an aquifer by precipitation, which percolates downward through soil and rock.surface runoff Water flowing off the land into bodies of surface water reliable runoff Surface runoff of water that generally can be counted on as a stable source of water from year to year.
Figure 15-2Page 307
Available Freshwater Supply
• The management of water’s supply, renewal, and use is a huge twenty-first century challenge. Only about 0.01% of the earth’s supply of water is available as freshwater in the soil, in usable groundwater, water vapor, lakes and streams, but this supply is recycled.
• The hydrologic cycle collects, purifies, recycles, and distributes the world’s freshwater supply.
• The world’s demand for water now requires 54% of the world’s reliable runoff of surface water. We could be using 70–90% by 2025. In some places, usage rates are exceeding the reliable runoff available.
Water Uses
Water Use Activities
o How much water do you use?
o Water Loss Drop By Drop
The Unequal Distribution of Water
Transfer of Heat Energy
Temperature is the measure of the average speed of motion of the atoms, ions, or molecules in a substance or combination of substances at a given moment.
Heat is the total kinetic energy of all the randomly moving atoms, ions, or molecules within a given substance, excluding the overall motion of the whole object. Heat always flows spontaneously from a hot sample of matter to a colder sample of matter. This is one way to state the second law of thermodynamics.
Bill Nye -Heat
ConvectionHeating water in the bottom of a pan causes some of the water to vaporize into bubbles. Because they are lighter than the surrounding water, they rise. Water then sinks from the top to replace the rising bubbles. This up and down movement (convection) eventually heats all of the water.
Heat from a stove burner causes atoms or molecules in the pan’sbottom to vibrate faster. The vibrating atoms or molecules then collide with nearby atoms or molecules, causing them to vibrate faster. Eventually, molecules or atoms in the pan’s handle are vibrating so fast it becomes too hot to touch.
Conduction
Radiation
As the water boils, heat from the hot stove burner and pan radiate into the surrounding air, even though air conducts very little heat.
Global Air Circulation and Transferring Heat
Water’s (Oceans) Role in Transferring Heat
Ocean Currents
Following Water’s Journey – The Thermohaline Conveyor
North Carolina River Basins
Click on the Map….it will take you to an interactive website exploring North Carolina River Basins
Figure 15-7Page 310
Highly likely conflict potential
Substantial conflict potential
Moderate conflict potential
Unmet rural water needs
Wash.
OregonIdaho
Nevada
California
Utah
Montana
Wyoming
Colo.
N.M.
N.D.
S.D.
Neb.
Kansas
Oak.
Texas
Water hot spot areas in 17 western states that by 2025 could be faced with intense conflicts and “water wars” over competition for scarce water for urban growth, irrigation, recreation and wildlife.
Water Issues in the United States
Colorado River Basin / California’s Demand For Water
The Colorado River is 1,400 miles long and has been altered by 14 major dams and reservoirs to the point that water rarely reaches the Gulf of California now. This endangers many species that spawn in the river system and has led to increased salt contamination of aquifers near the coast.
Water demand in the desert
Dam ImpactDams vs. Salmon – Pacific Northwest
Large lossesof water throughevaporation
Flooded landdestroys forestsor cropland anddisplaces people
Downstreamflooding is reduced
Downstreamcropland andestuaries aredeprived ofnutrient-rich silt
Reservoir isuseful forrecreationand fishing
Can producecheap electricity(hydropower)
Migration andspawning ofsome fish aredisrupted
Provides waterfor year-roundirrigation ofcropland
Figure 15-9 Page 313
Dam Trade-offs
advantages
disadvantages
The Everglades – The River of Grass
An Ecosystem Dying of Thirst
Much of the everglades have been drained for agriculture and urban development
Salton Sea and the Aral Sea Disaster
Aral Sea
GroundwaterOverdrafts:
High
Moderate
Minor or none
Figure 15-16 Page 320
Groundwater
Ogallala Aquifer
Figure 15-8Page 311
Stress on world water supplyIncreasing numbers of people relying on limited runoff produces a low per
capita availability of water, which leads to water stress.
Water stress comes when the volume of reliable runoff per capita drops to below 60,000 cubic feet/year.
Water scarcity occurs when per capita water availability falls below 35,000 cubic feet per year.
1. Poor people live in hydrological poverty—they have no access and/or cannot afford clean water at a reasonable cost.
2. Freshwater supply can be increased by building dams to store water for later use, importing water from elsewhere, using groundwater, and utilizing desalination processes.
3. People in developed countries live near water supplies, but people in developing countries must make do with what is available.
4. Most people believe that everyone has a right to clean water.
Too Little Water
Solutions:
Dams
Desalinization projects
Groundwater decontamination
Cloud seeding
New technology: Z-weed
Most water resources are owned by governments and managed as publicly owned resources, but a number of governments are hiring private companies to manage them.
There have been mixed results, and the lesson learned is that governments need to maintain strict oversight of these contracts.
Two possible problems with a totally privatized water system are:
1. Private companies have an incentive to use as much water as possible rather than conserve it
2. The poor will continue to be left out because they can’t pay for the water.
Water Politics
Gravity Flow(efficiency 60% and 80% with
surge valves)
Water usually comes from an aqueduct system or a nearby river.
Drip Irrigation(efficiency 90-95%)
Above- or below-ground pipes or tubes deliver water to
individual plant roots.
Center Pivot(efficiency 80% with low-pressure
sprinkler and 90–95% with LEPA sprinkler)
Water usually pumped from underground and sprayed from
mobile boom with sprinklers.
Irrigation Methods
Conserving water Composting toilets
Cisterns & rain barrels
Floodplain
Levee Floodwall
Dam
Reservoir
Too Much Water
• New Orleans (2005)– After Katrina
• Missouri Flood 1993
Efforts to reduce flooding risk include:
1. Channelization – straighten and deepen streams
2. Building levees or flood walls
3. Buildings dams (another dam project)
• Clearing of forests in the Himalayas and clearing mangrove swamps on the coasts has increased flooding in Bangladesh.
• Great floods used to occur about every 50 years or so, but since the 1970s, they now occur about every 4 years.
• Cutting of forests in the Himalayan foothills increased runoff and carried away vital topsoil.
• Floods and cyclones have destroyed many crops and have killed thousands of people and left many others homeless.
• Poor families have cleared many mangrove swamps for fuelwood, farming, and aquaculture ponds for raising shrimp, which ultimately led to greater flooding with the loss of those wetlands.
Bangladesh: Living on the floodplains –Danger for the poor
Flooding – video clip
Deforestation’s Impact on the hydrologic cycle and aquatic ecosystemsErosion from deforestation - Madagascar
